The present invention relates generally to cathode-ray tube (CRT) displays and, more particularly, to a circuit for driving a selected number of elements of field emission arrays on the cathode of a CRT to thereby provide a linear range of brightnesses to the individual pixels of the display.
A cathode-ray tube (CRT) is a particular configuration of vacuum tube useful in a wide variety of electronic applications, most commonly as a display device in television receivers, oscilloscopes and computer monitors. The primary function of a CRT is to convert the information contained in an electrical input signal to electron beam energy, and to convert that energy into light energy so as to provide a visual display of the input signal information.
In a basic cathode-ray tube, electrons are emitted from a thermionic cathode and controlled by control grids. The beam of free electrons is accelerated through an anode section by magnetic or electrostatic attraction forces, and is deflected, typically on horizontal and vertical axes, by a magnetic deflection coil or by electrostatic deflection plates. The electrons of the beam strike a light-emitting phosphor-coated surface, emitting visible light for a short interval of time.
The input signal containing the information to be displayed is applied between the control grids and the cathode. However, the relationship between the beam current and the control voltage (commonly referred to as the gamma characteristic) is a very nonlinear function, and relatively complex compensation circuits are required to be coupled between the input signal and the control grids in order to provide a linear range of display intensities.
In recent years, the widespread activity in the area of flat panel displays has spawned the development of non-thermionic cathodes, illustratively, field emission arrays which may be of the type developed at SRI International, Menlo Park, Calif., which are commonly referred to as Spindt cathodes, after Charles A. Spindt.
The use of an array of field emission cathodes in a cathode-ray tube, in place of the conventional thermionic cathode, would appear to provide certain advantages. In particular, the use of field emission cathodes allows much higher current densities. Additionally, elimination of a heater element may be expected to extend the life of the tube.
On the other hand, however, a field emission cathode is even more non-linear with respect to the emission of electrons in response to the driving signal than its thermionic counterpart, and an even more complex compensating circuit is required to provide a linear range of CRT luminances over the range of input signal voltages. It is clear that there exists the need for a simpler method of providing linear brightness control of a CRT having a field emission array cathode.